In one of Hollywood's saddest stories, "Gilligan's Island" beauty DAWN WELLS has fallen on terrible times – she's flat broke, smokes pot all day and is about to lose her home.

Once the fantasy girl of millions, the now 74-year-old actress – who portrayed Mary Ann, the sexy but wholesome girl-next-door – is so far behind on her mortgage and tax payments that the bank intends to auction off her home.

Dawn's comfortable house in Toluca Lake, Calif., has four bedrooms, three baths, a swimming pool and guest house. It's valued at $700,000.

"She's still the same sweet person she has always been, but she's more concerned with smoking pot than getting an acting job," a close friend told The ENQUIRER.

"Dawn loves to sunbathe topless in her backyard. Between catching rays, getting high and sleeping, her days are full. She'd rather live this kind of life than go out and get a job."

Now, her career is up in smoke.

Dawn got her start in showbiz after being crowned Miss Nevada in 1959 and competing in the Miss America pageant. She moved to Hollywood and began booking jobs almost immediately.

The dark-haired stunner had parts on "77 Sunset Strip," "Wagon Train," "Maverick" and then rocketed to fame on the legendary "Gilligan's Island" sitcom, starring BOB DENVER.

After Dawn came back ashore, she worked in nearly 100 plays, mostly traveling in musical theater productions throughout the '70s and '80s.

She also created "Mary Ann's Gilligan's Island Cookbook" and became a spokeswoman for several companies. But she's hardly worked at anything in the last few years.

"Dawn is a very nice woman, but she is just a pothead who didn't seem to take anything seriously, and now it's too late," confided the friend.

"She had a lot of tax liens and was forced to file bankruptcy in 2009. She's been in financial trouble for a long time, and it's finally come to a head."

A rep for Dawn said that she admits smoking pot in the past but has not done it recently.

In any case, the "Gilligan's Island" star is struggling to stay afloat.

"Dawn has already moved out of her house and into a small apartment," said the friend. "She knows there is no hope of saving her home. No one even knows exactly where she moved or what she's doing."

The actress was married to producer Larry Rosen from 1962 to 1967, but they had no children.

Said the friend: "Sadly, she's basically by herself."